1. Field of the Invention
The present invention relates to a database system having a database file comprising a plurality of storage units. It particularly relates to a database system characterized by its control to load the definition data for the storage units.
2. Description of the Prior Art
In a conventional database system, a database file, which is an external storage medium to store data, is divided into a plurality of areas referred to as "storage units". When utilizing a database file, storage units are established in the database file first. Upon establishment of such storage units, their sizes and locations, data attributes and the number are stored as definition data in a definition data file.
When processing for the above database file is started, the definition data for the storage units are loaded from the definition data file to a definition data storage. With reference to the definition data loaded at the definition data storage, the database system opens, updates/retrieves and closes the database file.
Such a conventional database system loads the definition data from the definition data file to the definition data storage when the database file processing starts. If storage units are reestablished (with a change in the number of storage units, for example) between the start of processing and opening of the database file and the definition data are changed, the definition data storage keeps the definition data before such reestablishment. This causes the system to open, update, retrieve and close the database file with reference to the definition data before data concerning reestablished storage units is stored in the definition data storage. In other words, the system tries to process the database file with reference to the definition data, which is different from the actual structure of storage units.
If the storage units are differently structured from the definition data referred to, the database file can be hardly opened. Even if it can be opened, it cannot be updated or retrieved properly. Further, if the database file is updated based on incorrect definition data, the database file may be destroyed in the worst case.